Tool for the repair of piano hammers



Sept. 29, 1959 H. E. HALE TOOL FOR THE REPAIR OF PIANO HAMMERS 7 Filed June 7, 1957 I INVENTOR.

HAROLD E. HALE BY oae flammfifm ATTORNEYS United Sites 2,906,067 TOOL FOR THE REPAIR OF PIANQ I i a :l J RS 1 Claim. (Cl. 51-47(9) In the repair and servicing of pianos, it is necessary from time to time to file or grind the felt hammer surfaces where they contact the strings of the piano, and thus remove the dirt which has gradually accumulated and encrusted the felt and remove any unevennesses caused by repeated blows on the strings. Cleaning and smoothing the surface results in a better tone. Surfacing the hammers requires skill and experience and if improperly done results in injury to the piano. Sometimes this work is done with a file and sometimes with a portable sander drum carried on the shaft of a motor tool which rotates the sander drum rapidly. To guide the drum sander along the surface of the hammer which is to be refinished without injuring it requires skil1 and experience; otherwise the cut may be too deep or uneven and the hammer injured.

My present invention provides a guide which can be put on a motorized drum sander and can be adjusted so that the sander drum will remove only the required thin layer from the surface of the hammer and cannot gouge into the face of the hammer and thus injure it. The drum sander guide embodying my invention is easily adjustable to increase or decrease the depth of cut to that which is most satisfactory under the particular circumstances.

The invention will be understood from the following description taken in connection with the accompanying drawings, in which:

Fig. 1 is a motor driven drum sander to which my novel sander guide is applied.

Fig. 2 is an end view of the sander guide shown in Fig. 1.

Fig. 3 is a side elevation of the sander guide.

Fig. 4 is a section on line 44 of Fig. 2 looking in the direction of the arrows.

Fig. 5 is a section on line 55 of Fig. 4 looking in the direction of the arrows.

In the drawings, the body enclosing the motor of the drum sander is shown at 10. At 11 is shown the control switch. At 13, see particularly Fig. 4, is shown the cylindrical housing and at 14 the drive shaft. At 16 is shown the sander drum mounted on the end of the shaft 14. This drum rotates rapidly and has an abrasive surface, e.g., emery, and therefore is an effective cutting tool by which the surface of the hammer may be removed. The cylindrical surface of the housing 13 is concentric with the axis of the drive shaft 14 and of the sander drum 16.

Mounted on the housing 13 is a guide 17. This guide 17 is split at 18 (see Fig. 3) and may be slipped over the housing 13 and clamped in place by a flexible clamping ring 19, there being a clamping screw 22 to draw the clamping ring tightly about the split end of the guide 17 and clamp it immovably about the housing 13. The guide 17 has a cylindrical bore 20 but this bore is not concentric with the axis of the shaft 14 or the housing 13. This eccentricity will be seen from Fig. 5 where the bore 20 is shown to be off-center from the axis 21 of the atent drive shaft 14. The eccentricity of the bore 20 will also be seen from Fig. 4 where the wall at a is shown to be thicker than the wall at b, also that the space 0 is larger than the space on the other side of the sander drum 16.

The guide 17 (see Fig. 1) is slabbed off as shown to form two guide surfaces 24, 24 and a guide shoulder 25. There is an open space 26 between the two guide surfaces 24, 24 and the surface of the sander drum 16 is ordinarily slightly below that of the guide surfaces 24, 24 so that the drum 16 can contact the felt surface of the hammer as the tool is moved along it. During this movement the shoulder 25 is held against the side of the hammer and is guided by it.

The amount by which the hammer will protrude through the space between the two guide surfaces 24, 24 and consequently the depth of cut which the sander will take in the face of the piano hammer can be adjusted with extreme accuracy by rotating the guide 17 on the housing 13. To do this the clamping screw 22 is loosened and the adjustment is made. Thereafter, the clamping screw 22 is tightened and the guard is held in place immovably on the housing 13. This adjustment is such that the depth of cut of the sander drum 16 can be adjusted to within a thousandth of an inch or even less. In practice, however, it is found convenient to tighten the clamp enough to hold the guides 17 in place by friction and yet allow the piano tuner to rotate the guide 17 on the housing B as required to adjust the tool for hammers having different curvatures.

In the operation of my device the position of the sander roll 16 with respect to the guide surfaces 24, 24 is adjusted as described so that the required depth of cut for each hammer will result. The clamping screw is then tightened to the extent desired. The sander drum 16 is then passed along the surface of the hammer of the piano with the guide shoulder 25 resting against the side edge of the hammer. This removes a thin layer of felt from the working surface of the hammer, the thickness of this layer depending upon the adjustment of the guide 17 circumferentially about the housing 13. It is found that in practice this can be done easily and the hammer resurfaced quickly and accurately and without the skill which is necessary when the hammer surface is to be refinished by the use of a file or sandpaper.

I claim:

In a portable tool for truing the felt surface of piano hammers and in combination, a housing having a cylindrical shaped surface, a grinding wheel having a rota tional axis which is concentric with the cylindrical surface of said housing, said wheel being mounted on a shaft which is rotatably mounted in the housing and has an axis of rotation concentric with said cylindrical surface, a hollow guide sleeve having an eccentric bore receiving said cylindrical surface of said housing for rotation of said guide on and with respect to said housing, said grinding wheel being located beyond the end of said cylindrical surface and said guide extending beyond the end of said surface over said grinding wheel, said guide having an opening in the side thereof exposing a portion of the peripheral surface of said grinding wheel, the edges of said opening comprising guide surfaces, the edges of said opening and hence the opening being movable radially with respect to the center axis of said grinding wheel surface by rotation of the guide on the cylindrical surface of the housing due to the eccentricity of said bore, whereby the depth of the cut of said grinding wheel in a surface against which the guiding surfaces of said guide are held can be varied by rotating the guide.

References Cited in the file of this patent UNITED STATES PATENTS 

